Retrieve and expose parts of mutipart SMS messages as they come

Sometimes, parts of multipart SMS messages take some time to arrive.

I am writing an SMS application and I would like to display the parts that have been received so far while the message is still coming. I had a phone doing this before smartphones became ubiquitous and that means being able to read most of the message vs not being able to read the message at all when a part is missing and never coming (on a bad network for instance).

I actually found myself saving a long text message using AT commands because ModemManager was not retrieving it.

Since parts can be received unordered, the parts could be exposed as an array with empty values for missing parts. The size of the array would be the total number of expected parts.

I feel like this feature might provide a nice way to fix #428, removing parts from the modem as they come instead of retrieving everything from the modem when all the parts have been received. It could also fix #377

Is this feature conceivable in ModemManager? If no, what would be the drawbacks preventing from considering it?